Calcium electrode studies: These studies involve the application of ion-exchange calcium electrodes to clinical, physiologic and physico- chemical problems in calcium metabolism. Specific projects include studies of protein-binding by serum proteins in normal and pathologic states, pH and temperature nomograms for serum ionized calcium (Ca ion), effects of Ca ion on gastric secretion, and kinetic models for salivary secretion. Ammonia electrode studies: These studies involve the application of a recently-developed ammonia electrode to biologic systems. Specific projects include ammonia in urine, sweat and saliva, and the physico- chemical state of ammonia in human serum and whole blood. Small intestinal absorption-secretion studies: The objective of these studies (dog and rabbit) is to define the role of ion-exchange mechanisms in cation and anion transport, the effects of hormones, and the state of hydration of the animal.